In many water clarification treatment processes the separation of solids from liquid(s) is effectuated at least in part by filtration. The filtration may be effectuated through a bed of granular media or through a membrane or septum with or without a filter aid. A typical filtration aid, such as diatomaceous earth, is often applied as to slurry to a porous septum, forming a precoat that strains, or helps strain, the suspended solids in the liquid passed through. Granular media or filtration aids may become to a degree admixed with the solids being strained, and for some processes, particularly those in which the solids are collected for subsequent use or recycling, the granular media or filtration aid admixture with the collected solids or sludge is undesirable. Further processing to separate the material used to strain the solids from the solids collected generally is uneconomical. For instance, in food processing industries, the solids collected from process water, that is, water used for washing the raw foodstuff, conveying the products from one process area to another, extracting and the like, may be substantially derived from the foodstuff itself and hence be useful material for producing inexpensive food matter, such as animal feed or the like. Granular material, such as sand, diatomaceous earth, and the like may be undesirable components of such collected solids, and yet the end use of such solids does not justify the expense of separating the granular media from the solids.
Such filtration processes are often preceded by chemical water treatments and other physical treatments. For instance, coagulant or flocculant chemicals are added to the water being clarified to assist in concentrating the solids to be removed. Where the solids are light, i.e., have specific gravities near, or less than, the liquid in which they are suspended, air-flotation way be used to concentrate the solids by floating them to the surface by air bubbles, rather than concentration by settling. In dissolved air flotations systems (DAF systems) the water being clarified is pressurized and supersaturated with air. Upon reduction of pressure, the air comes out of solution, forming microbubbles which float the solids upward to the surface. In DAF units often a chemical treatment will be added at the point in the system where the bubbles are forming and contacting the solids to be removed. Solids concentrated by air flotation are generally referred to as "floats" and as such floats may be subjected to filtration, forming a "cake", i.e., the build-up of solids on the surface of the filter or filter bed.
As mentioned above, the end use of the solids being separated may render the use of certain granular media undesirable. Where the solids being separated are generally organic in nature, there may be a need for a granular media that is likewise organic in nature, for instance in the filtration of solids from the process water of food processing plants. Such granular media must, however, to be commercially feasible meet the industry standards both as to its ability to strain the solids and as to passing the liquid, usually water, through. Concentration of the solids, reducing the water content, is an important feature, as is the reduction of suspended solids in the water that passes through.
It is the object of the present invention to provide a filtration process, and filter media therefor, wherein the filter media becomes incorporated into the cake substantially without increasing the inorganic content thereof, while providing clear filtrate and high density cake. These and other objects of the present invention are described in more detail below.